Immune function has been shown to be altered in adults with major depressive disorder (MDD) but has not been investigated in depressed children. Psychoimmunologic studies with depressed adults have demonstrated changes in range of immune functions in MDD in adults that are age-related and associated with the severity of depressive symptoms. The most marked immune changes were found to occur at the extremes of the age range. The extent to which depressive disorders in children are comparable to MDD in adults is not known. If MDD in childhood shares pathophysiologic features with adult MDD, children with MDD may be predicted to show changes in immune functions comparable in nature to that found in depressed young adults and possibly of greater magnitude. Psychobiological investigations of depression in prepubescent subjects have suggested that, as in adults, there may be neuroendocrine alterations in depressed children that may contribute to regulation or modulation of immunity. The proposed investigation of immune processes in prepubescent subjects with MDD will begin determine if immune function in physically health, medication free, prepubescent children with major depressive disorder is different from that of health matched controls. In addition, the proposed research will begin to explore the relationship between immune function in childhood depression and such factors severity of depression and gender. Children referred for depression and health matched controls will be evaluated for MDD using the Diagnostic Interview for Children-Revised (DISC-R). Severity of depressive symptomatology will be assessed using the Children's Depression Rating Scale (CDRS) and the Children's Depression Inventory (CDI) by the applicant and a research assistant. A battery of immune assays will be performed for depressed children and controls including quantitative and functional measures. Data on 20 patient/control pairs will then be analyzed utilizing t-test, ANOVA, and multiple regression techniques.